Fix multiline display equations in HTML

CHANGELOG.md

@@ -14,6 +14,8 @@
 
 * ![Bugfix][badge-bugfix] Doctests now correctly handle the case when the repository has been checked out with `CRLF` line endings (which can happen on Windows with `core.autocrlf=true`). ([#1516][github-1516], [#1519][github-1519], [#1520][github-1520])
 
+* ![Bugfix][badge-bugfix] Multiline equations are now correctly handled in at-block outputs. ([#1518][github-1518])
+
 ## Version `v0.26.1`
 
 * ![Bugfix][badge-bugfix] HTML assets that are copied directly from Documenters source to the build output now has correct file permissions. ([#1497][github-1497])
@@ -740,6 +742,7 @@
 [github-1510]: https://github.com/JuliaDocs/Documenter.jl/pull/1510
 [github-1511]: https://github.com/JuliaDocs/Documenter.jl/pull/1511
 [github-1516]: https://github.com/JuliaDocs/Documenter.jl/issues/1516
+[github-1518]: https://github.com/JuliaDocs/Documenter.jl/pull/1518
 [github-1519]: https://github.com/JuliaDocs/Documenter.jl/pull/1519
 [github-1520]: https://github.com/JuliaDocs/Documenter.jl/pull/1520
 

src/Writers/HTMLWriter.jl

@@ -1762,9 +1762,9 @@ function mdconvert(d::Dict{MIME,Any}, parent; kwargs...)
         # unwrap it first, since when we output Markdown.LaTeX objects we put the correct
         # delimiters around it anyway.
         latex = d[MIME"text/latex"()]
-        equation = false
-        m_bracket = match(r"\s*\\\[(.*)\\\]\s*", latex)
-        m_dollars = match(r"\s*\$\$(.*)\$\$\s*", latex)
+        # Make sure to match multiline strings!
+        m_bracket = match(r"\s*\\\[(.*)\\\]\s*"s, latex)
+        m_dollars = match(r"\s*\$\$(.*)\$\$\s*"s, latex)
         if m_bracket === nothing && m_dollars === nothing
             out = Utilities.mdparse(latex; mode = :single)
         else

test/examples/src/man/tutorial.md

@@ -433,3 +433,39 @@ or wrapped in `$$ ... $$`:
 ```@example showablelatex
 LaTeXEquation(raw"$$\begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix}$$")
 ```
+
+---
+
+Extra tests for handling multi-line equations ([#1518](https://github.com/JuliaDocs/Documenter.jl/pull/1518)):
+
+
+```@example showablelatex
+LaTeXEquation(raw"""
+\[
+    \left[
+        \begin{array}{rr}
+            x & 2x
+        \end{array}
+    \right]
+\]
+""")
+```
+
+```@example showablelatex
+LaTeXEquation(raw"""$$
+\begin{bmatrix}
+    1 & 2 \\
+    3 & 4
+\end{bmatrix}
+$$""")
+```
+
+Without `raw""` strings we have to double-escape our `\` and `$`:
+
+```@example showablelatex
+LaTeXEquation("\\[\\left[\\begin{array}{rr} x & 2x \\\\ \n y & y \\end{array}\\right]\\]")
+```
+
+```@example showablelatex
+LaTeXEquation("\$\$\\begin{bmatrix} 1 & 2 \\\\ \n 3 & 4 \\end{bmatrix}\$\$")
+```